Introduction

The nematode database as presented here is a combined list of Aphelenchida, developed by Dr Mike Hodda, CSIRO Entomology, Canberra, and marine nematodes compiled by Rebecca Gray, Dr Warwick Nicholas, and Dr John Trueman, School of Botany and Zoology.

[Introduction to the Checklist of Free-living Marine and Estuarine Nematodes from Australia, Macquarie Island and Heard Island, by Dr Warwick L. Nicholas, Australian National University]

IntroductionNematodes are abundant in marine sediments, dominating the coastal, and sub-littoral and estuarine marine meiofauna, inhabiting even the deepest ocean trenches. They move easily through mud and sand, but are poorly adapted to swimming so that they do not occur in the plankton except as parasites or commensals of other animals. They are essentially aquatic, but require only a thin film of water so that they can move through damp sand and soil. They play a similar dominant role in terrestrial ecosystems. The ability of some species to tolerate dehydration enables them to inhabit arid deserts while others, that can survive freezing conditions, inhabit polar and alpine regions, in both cases becoming active and reproductive when conditions temporarily provide free moisture.

Nematodes are usually easily recognised by their sinuous mode of locomotion and absence of locomotory appendages. It is often said that they all look alike, but this is only very superficially true. A few marine nematodes depart from this general rule, progressing by means of tube feet. Most are small and transparent so that, under high magnification, a great diversity of internal structure is evident and provides the basis for taxonomic descriptions. The best known to the non-specialist are the great variety of larger parasites of man and domestic animals (round worms). Others are very important in agriculture as plant endo- and ectoparasites. However, the greatest diversity and highest populations are found in marine sediments, largely unknown and unsuspected even by biologists because of their small size (generally less than 1 mm long) and obscure location.

Not only do free-living nematodes outnumber other animals in marine sediments, but also exceed other meiofauna in total biomass. The phylum Nematoda is probably second only to the phylum Arthropoda in numbers of different species, though, since most nematodes have yet to be described, any estimate of the numbers of species can only be very indirect. Hyman in her 1951 text book on Aschelminths estimated 50,000 species and no one in the last 60 years has provided a better estimate. Andrassy (1992) gave a census of described species and genera of free-living nematodes (11,000 species described) and from this estimated 100,000 species total. Lambshead (2004) estimated 1 million to 100 million using a variety of extrapolative and interpolation methods on ecological data sets.

Bastian in his 1865 monograph on free-living nematodes described 100 new species, including some that are marine. His monograph described and illustrated 17 genera of marine nematodes, re-naming some previously described by other European nematologists. After 1895, numerous European nematologists described many marine nematodes, some from sub-littoral habitats. Notable, because of his contributions to the classification of marine free-living nematodes, were two monographs by Filipjev (1918, 1921) on nematodes from the Black Sea. Both of these works are in Russian, but they have been translated into English and republished by the Israel translation program (Raveh 1968, 1970). Many of Filipjev's orders are still valid.

In 1888, Nathan Cobb, from Yorkshire in England, travelled by sea to Australia, collecting marine nematodes en route, including Chromogaster purpurea(= Siphonolaimus purpureus) from Port Adelaide (Cobb 1894), which must be the first marine nematode from Australia to be recorded. Cobb settled in Wagga Wagga and Sydney for some time, describing a number of marine and terrestrial nematodes from the neighbourhood, in the Proceedings of the Linnean Society of New South Wales (Cobb 1894, 1898). Later, he emigrated to the United States where he became a famous plant nematode pathologist, but he retained an interest in free-living nematodes. In a monograph (Cobb 1920) he described 100 new nematodes from many parts of the world (but not from Australia), the great majority marine. Almost all the species were type species of new genera, many of which have subsequently been found in Australia. Cobb championed re-naming the phylum 'Nemata', on dubious grounds, which name has had very limited following and is destined to lapse.

Cobb's taxonomic work, together with that of later American and European nematode taxonomists, shows that many nematode genera have worldwide distributions. To what extent this is also true of species remains to be seen, but undoubdtedly some Australian species have cosmopolitan distributions. When studying collections, it is often possible to recognise several different species in a single genus without being able to name species. Reliable identification requires multiple specimens and many statistically valid measurements, and, because of this difficulty, it has become an accepted practice in many ecological investigations to identify genera (which can be done from morphological characters), but to label species within genera as sp.1, 2 and so forth.

There are positive and negative consequences of this cosmopolitan distribution of genera. The pictorial key to genera provided by Platt and Warwick in each of their reviews of the marine nematode fauna of the British Isles (Platt & Warwick 1983, 1988; Warwick, Platt & Somerfield 1998) can be used to identify most of the genera found in the Australian marine fauna. It is important to note that not all Australian genera are included in their pictorial key. At the present time, the marine nematode fauna of New Zealand and Indonesia are virtually unknown so that it is impossible to say whether genera and species as yet only described from Australia have wider distributions. The closest well-known marine nematode faunas come from East Africa, South Africa, The Maldives, Chile, Oregon and British Columbia.

A negative consequence of the worldwide distribution of species and genera is that taxonomists working on the Australian fauna need to consult the world taxonomic literature in English, French, Italian, German, Spanish and Russian, before publishing descriptions of new taxa. In this respect, Gerlach and Riemann's (1973/1974) taxonomic checklists (in English) of all published taxonomic descriptions of aquatic nematodes up to 1974, with complete citations of the literature, are invaluable. Descriptions of Australian marine nematodes have almost all been made by visting European taxonomists. An unfortunate consequence is that most type material is in foreign museums, and though these museums will often lend some type material, the Australian taxonomist may need to visit the Smithsonian Museum in Washington, The Natural History Museum in London, the University of Ghent in Belgium, the Bremerhaven Institute of Marine Science in Germany and the Muséum National d'Histoire Naturelle in Paris, to name but a few.

Irwin-Smith (1918) described four species of Draconematidae from Port Jackson. Otherwise the only permanent Australian resident marine nematode taxonomists are myself [WL.Nicholas] and past and present colleagues at the Australian National University in Canberra. A few Australian type specimens are located in Australian State Museums. The CSIRO Division of Entomology in Canberra has a type collection of free-living nematodes, currently supervised by Dr M. Hodda, who studied marine nematodes for some years, but who currently studies terrestrial and freshwater species. Specimens should be mounted on slides in anhydrous glycerol, the internationally accepted practice.

B.G. and M.B. Chitwood published very comprehensive and copiously illustrated accounts of the Nematoda in the 1930s and 1940s, more recently re-published as an Introduction to Nematology, Consolidated Edition (1974). The Chitwoods introduced the division of the phylum Nematoda into two classes, Aphasmidia and Phasmidia, based on differences in the 'excretory systems', a division recognised until almost today. Later, B.G. Chitwood (1958) recognised that the name Phasmidia was very close to the name of an insect group (Phasmida) and re-named the two classes as Adenophorea and Secernentea, respectively. Hyman, at the American Museum of Natural History, produced an influential series of monographs, The Invertebrates. In Volume III (1951), Hyman included Nematoda as a class of the phylum Aschelminthes, with Rotifera, Gastrotricha, Kinorhyncha, Priapulida and Nematonorpha as other classes. Many text books of invertebrate zoology have found it convenient to follow this classification, although a phylogenetic basis for the classification was always doubtful and most nematologists have continued to consider the Nematoda as a Phylum.

Lorenzen (1981) published a monograph (in German) in which the Adenophorea was subject to a strict cladistic analysis to give a purportedly phylogenetic classification of the Adenophorea. An English translation was published by Platt (1994). It so happens that most free-living marine and estuarine nematodes belong to the Adenophorea, while most terrestrial, and freshwater nematodes and many parasitic nematodes belong to the Secernentea. Lorenzen's classification has been used by most marine nematologists.

The terrestrial free-living nematode Caenorhabditis elegans has been the key to advances in molecular biology, and was the first metazoan to have its genome completely sequenced. Molecular Biology will transform phylogenetics and has already shown that many previous classifications of the Nematoda (which were justified by and based on the practical need to identify animal and plant parasites) lack any phylogenetic basis. Paul De Ley and Mark Blaxter (2001) published a comprehensive phylogenetic classification of the Nematoda to family level, based largely, but not entirely, on SSU rDNA sequences. The first checklist of free-living nematodes, including some records of marine nematodes, was Johnston's (1938) publication. The previous checklist in this series recording marine free-living nematodes from Australian waters was Greenslade's (1989) publication. It listed 263 species from 119 genera and 38 families. The Nematode classification adopted here has been updated, following Hodda (2007).

Acknowledgements

We thank ABRS for financial support and especially Alice Wells for her help in all phases of this project. The School of Botany and Zoology at the Australian National University provided accommodation and resources, and we acknowledge the many contributions of library staff at both the ANU and the CSIRO Black Mountain Library in Canberra.

Database Notes

This database is as complete as we have been able to make it, but some data remain missing and some conventional items have not been included. The coverage is of all Aphelenchida recorded from Australia, and all marine free-living nematodes from Australian waters including Australia's offshore territories, but in some cases early records from Antarctica have been included without our having been able to ascertain that the collection site falls within the Australian Antarctic Territory as afterward declared. Separate introductions to each of the 44 families are not included for the marine groups. Some few primary references are incomplete, and will be completed in a subsequent update.

Remarks

Re family CephalobidaePers. comm., Hodda (2007): 'This is a family consisting of a large number of species. The family occurs almost everywhere in soils and in invertebrates as parasites. Individual species and strains within species (particularly for the animal parasites) may be very restricted in distribution. The comments [under] "Aphelenchoides sp." apply here as well, only to a larger degree. It is almost impossible to tell whether something identified only as "Cephalobidae sp." occurs in any place other than that collected, and whether it may be harmful (to invertebrates) or not. Most are not harmful, but some may kill various invertebrates.'